The present invention provides a means for joining an optical fiber in light coupling alignment with an electrooptical device, such as a semiconductor laser, without the introduction of stresses that invariably result in element misalignment and degradation of coupling efficiency upon subsequent relaxation of such stresses. In particular, the invention provides a method of coupling an optical fiber to an electrooptical light emitter or transducer without employing any of the common practices of welding, soldering, or applying epoxy adhesives, each of which introduces a temperature gradient into the assembly, thereby promoting misalignment stress when the fiber-to-device assembly returns to ambient condition.
Currently, it is common practice to counter post-assembly misalignment, whether caused by stresses induced during assembly or encountered in use from fiber manipulation, by employing relatively massive physical structures to support and join a laser, for example, in simple butt end alignment with an optical fiber light guide. Typical of such structures is that depicted in U.S. Pat. No. 4,199,222. In such an assembly, the laser device is firmly mounted within close tolerance upon a precisely machined base of huge proportion in order to prevent any displacement of the device from a fixed datum. The optical fiber, likewise fixed within a substantial machined support member, is then brought into close alignment with the output laser facet, usually by threaded coupling of its support element with the base upon which the laser is mounted. Despite the great expense and time involved in the precise fabrication and manipulation of the assembly members, however, it is not uncommon that additional lens elements or post-assembly manipulation devices, as typically shown in U.S. Pat. Nos. 4,749,250 and 4,886,337, respectively, are required to obtain an initial optimum alignment for efficient coupling of light from the laser to the fiber. Thereafter, the mass and physical strength of the coupling structure are relied upon to maintain this alignment.
Not only are these prior practices extremely expensive and of questionable effectiveness, but the resulting size of the final coupling assembly, which is not uncommonly orders of magnitude larger than the laser device itself, in effect nullifies the otherwise outstanding advantage to be found in the minute dimensions of a semiconductor laser and prevents any practical application of these devices in multiple-laser arrangements for large scale integrated circuits. The present invention, on the other hand, provides stable and efficient coupling in a structure sufficiently small that the size advantages of the laser itself may be fully realized.